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From: David G. Johnston <[email protected]>
To: David Rowley <[email protected]>
Cc: Melanie Plageman <[email protected]>
Cc: Pg Hackers <[email protected]>
Cc: Robert Haas <[email protected]>
Subject: Re: EXPLAIN IndexOnlyScan shows disabled when enable_indexonlyscan=on
Date: Tue, 22 Oct 2024 17:50:56 -0700
Message-ID: <CAKFQuwbNOj4f6ar1+jkBFGhK+t6fNwzM0ygLh7GBFSxVGSO8TQ@mail.gmail.com> (raw)
In-Reply-To: <CAApHDvr_Ncavgr7z4xmXuStWCaQoE0=z2kZj6JiFku8DB1iBfw@mail.gmail.com>
References: <CAAKRu_atV=kovgpaLREyG68PB5+ncKvJ2UNoeRetEgyC3Yb5Sw@mail.gmail.com>
	<CAApHDvqAY6OVVPSRqGkcPExRKutCGzZPbhWm0EkORWGqLBWVxQ@mail.gmail.com>
	<CAKFQuwYx0m2O3rM=CF1nj6xuqNMTe-NPNOsue7chyqS_EjhKng@mail.gmail.com>
	<CAApHDvr_Ncavgr7z4xmXuStWCaQoE0=z2kZj6JiFku8DB1iBfw@mail.gmail.com>

On Mon, Oct 21, 2024 at 7:20 PM David Rowley <[email protected]> wrote:

> On Tue, 22 Oct 2024 at 14:46, David G. Johnston
> <[email protected]> wrote:
> > We should probably at least improve the documentation in 19.17.1; this
> interaction is apparently not self-evident.
>
> Yeah, I agree. The documentation could better reflect the current
> behaviour.
>
> Do you want to submit that in patch form?
>
>
Went with a slightly different wording that seems to flow better with the
xrefs I added between the two options.

David J.


Attachments:

  [text/x-patch] v1-0001-doc-Cross-reference-enable_indexscan-and-enable_inde.patch (2.2K, ../CAKFQuwbNOj4f6ar1+jkBFGhK+t6fNwzM0ygLh7GBFSxVGSO8TQ@mail.gmail.com/3-v1-0001-doc-Cross-reference-enable_indexscan-and-enable_inde.patch)
  download | inline diff:
From 8b9be4096352088ea22f114e68041fd09ee6e28c Mon Sep 17 00:00:00 2001
From: "David G. Johnston" <[email protected]>
Date: Tue, 22 Oct 2024 17:25:27 -0700
Subject: [PATCH] doc: Cross reference enable_indexscan and
 enable_indexonlyscan

Document that enable_indexscan controls the inclusion of all (normal
and index-only) index scan plan node types.  Note that index-only scans
can be independently disabled.

Note the implication of this in enable_indexonlyscan, that a setting of
"on" is ignored when all index scans types are disabled.

Left unwritten is the absence of a symmetric option to exclude normal
index scans while allowing index-only scans.
---
 doc/src/sgml/config.sgml | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 934ef5e469..04cbe7ac34 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5415,8 +5415,10 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </term>
       <listitem>
        <para>
-        Enables or disables the query planner's use of index-scan plan
-        types. The default is <literal>on</literal>.
+        Enables or disables the query planner's use of all index-scan related plan
+        types. The default is <literal>on</literal>. The index-only-scan plan types
+        can be independently disabled by setting <xref linkend="guc-enable-indexonlyscan"/>
+        to <literal>off</literal>.
        </para>
       </listitem>
      </varlistentry>
@@ -5429,9 +5431,10 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </term>
       <listitem>
        <para>
-        Enables or disables the query planner's use of index-only-scan plan
+        Set to <literal>off</literal> to disable the query planner's use of index-only-scan plan
         types (see <xref linkend="indexes-index-only-scans"/>).
-        The default is <literal>on</literal>.
+        The default is <literal>on</literal>. However, this setting has no effect if
+        <xref linkend="guc-enable-indexscan"/> is set to <literal>off</literal>.
        </para>
       </listitem>
      </varlistentry>
-- 
2.34.1

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  Subject: Re: EXPLAIN IndexOnlyScan shows disabled when enable_indexonlyscan=on
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